Purpose, Uses, and Applications of Mining Haul Truck Scales

FORCE Haul Mining Truck

Mining operations are being pressed to improve efficiencies, lower costs, maintain a high level of safety, and optimize equipment life. After strong gains over the last few years, commodity pricing has dipped more recently. Enjoying the benefits of strong pricing and ramping production, mining operations are now challenged with maximizing profits. Maximizing profits can be realized from various initiatives. Typically, this will be achieved through efficiency improvements and cost savings measures, while always assuring and maintaining the highest level of operational safety.

Prior to the downturn in the global economy in 2009, market demand resulted in the release of various models of “ultra-class” mining haul trucks. Ultra-class haul trucks are considered those that have a payload capacity of 300 US short tons or greater. By leveraging ultra-class trucks, mining operations can move more material per haul, hence improving efficiencies in haulage and loading.

Haulage and loading operations have process variations that are typically due to poor process control. These variances include the amount of material being moved per load, how it is loaded, how it is hauled and unloaded. Haulage and loading variances directly affect efficiency results in open pit operations, but they also directly affect costs. Hauling and loading efficiencies are going to be dictated primarily by the effectiveness of the shovel operator. This is determined by how they load the haul truck, and how fast. Under-loading the haul truck is not efficient, raising the cost of hauling and loading. One would rather over-load the haul truck to move more material in minimal runs, in lieu of under-loading and running more loads. The problems with persistent over-loading of haul trucks are the increased costs that impact the mining operation.  

Overloading of haul trucks imposes stresses on all the components and materials that support that load. These stresses lead to failures that need to be repaired or replaced, which are costly. These costs come in the form of vehicle maintenance, haul road maintenance, and among other concerns directly impact safety. The example shown on the previous page is the result of overloading a CAT797. This haul truck, which costs at least $3.0 million and is designed to carry 400 US short tons of material (363mt), was overloaded and resulted in a catastrophic failure.

The effects of overloading can also be realized from unbalanced loading. Unbalanced loading can apply more undue pressure and stress on one side of the haul truck than another. This will lead to premature failure and increased costs just as well as overloading a truck will.

Fleet Managers are being posed with lowering the cost of ownership of haul trucks. When stresses are imposed on the haul truck, they cause premature wear and failure of key components. Amongst the components and systems are the suspension, steering, brakes, and more importantly the tires. Off-the-road (OTR) tires, for the largest haul trucks, carry a price tag of $50,000 each (May 2010) to nearly $160,000 each (May 2011). Tires are estimated to account for nearly 35% of the truck’s operating costs. OTR tire suppliers are posed with high demand and low supply of the larger haul truck tires, requiring that mining operations maximize tire life in order to avoid equipment downtime. Overloaded trucks will add undue stress on tires causing premature wear, and in worst cases, overloading will cause the tires to become so hot that a fire will ignite inside the tire causing the tire to explode. Tire explosions are known to cause severe injuries, and in extreme circumstances death, to the driver or personnel near the equipment at the time of failure. Optimizing the amount of material being loaded into haul trucks, without compromising safety, is one strategy to improving efficiencies. This can be achieved by using properly calibrated on-board weighing systems that are integrated into shovels, loaders and haul trucks.

An effective method used in monitoring the amount of material being moved in a hauling operation, and calibrating on-board systems is to implement the use of platform scales. The specially designed platform scales are unique weighing systems designed to handle the extreme loads carried by haul trucks on mine sites. Typically, these weighing systems consist of 2 to 4 pads, depending upon the type and size of the haul truck being used at the site. Each pad weighs the load being applied at each tire along the front and rear axles of the haul truck. The systems are integrated on or near the haul road, in temporary or permanent installations, minimizing the amount of time required to divert the trucks from standard path of travel in order to capture weight data.

FORCE Mining Haul Truck Scale
FORCE Mining Haul Truck Weighing System

Depending on the make and model of the platform scales, weight data can be captured in static or dynamic mode. Static weighing requires the haul truck to be spotted onto the platforms, come to a complete stop and release brake pressure before moving onward with the haul. Other systems, such as the FORCE Mining Haul Truck weighing system, allow data to be captured in dynamic mode. Dynamic mode is “weigh-in-motion” which means that the haul truck does not need to come to a complete stop in order to capture data. This is key to operations that have permanently installed systems for monitoring daily hauling production by maintaining efficiencies allowing the truck to keep moving yet capturing data on a continuous basis.

Data is captured in a controller that prints, stores, and/or delivers the information on demand. Systems such as the FORCE have PC based controllers, which offer a tremendous amount of versatility. Operators can integrate RFID systems to automatically capture truck information along with additional information like the truck number, time, date, gross weight, tare weight, and net weight. One can apply solar power to run the systems, integrate laser volumetric scanning systems, and connect to wide and local area networks. Volumetric scanning, when combined with a scale can further define the amount of material being hauled and how it is loaded in the bed of the truck.

There are various acquisition and deployment options for mining haul truck platform systems available in today’s market. These systems can either be rented or purchased and if so desired a third party can come to the site and do a “weight study” utilizing the equipment. Weight studies are short-term programs that typically encompass one entire week. A set of scales are deployed to the site and trucks are re-routed over the scales as data is sampled over a duration of time. At the end of the sampling period, the findings are reported to the mining operation. In some cases, the findings are presented to management in a formal presentation showing detailed results of the study.

Several companies offer weight studies as a fee-based service. Historically OTR and haul truck manufacturers have offered weight studies to their customers. Originally used in root cause analysis when equipment failures occurred, the scope of weight studies has expanded to other purposes. Purposes include onboard system calibration, operational analysis, and safety analysis among others.

Weight studies may tend to have inherent deficiencies which have been known to cause poor results, offering inaccurate findings from the data captured. Weight study service suppliers have noted cases where a limited amount of haul trucks from a fleet were used for weight studies skewing conclusions drawn from the data. In other cases, operators of haul trucks, loaders, and shovels have modified their processes in order to optimize their performance to avoid being identified for poor performance. Thus, the data shows results that are not in accordance with true day to day operations.

FORCE Mining Haul Weight Study
FORCE Mining Haul Weight Study

For operations that are keen on monitoring daily operational performance, a set of scales are acquired and deployed into the haul road path, where all trucks are directed over the scales at every haul. This allows the mine to monitor daily haulage and loading performance, adjust onboard systems as needed, optimize loading to avoid over-loading and/or uneven loading, and assure safe loading and hauling volumes are being moved throughout the site.

Optimizing haulage and loading efficiencies are important to mining operations. Achieving the highest level of haul truck equipment up-time and life are imperative. Minimizing operating and equipment maintenance costs are crucial to improving margins. Maintaining a safe hauling environment is paramount to all mining operations. All these objectives can be achieved using mining haul truck scales. The advantages gained by leveraging mining haul truck scales will improve efficiencies, lower costs, and assure a safe environment in loading and hauling operations.

Southwestern Scale provides leading-edge weighing solutions and services to the mining industry in Arizona and the Southwestern United States by providing mining scales that help companies optimize operational efficiency, production control and promote safety. All of our scale technicians are MSHA certified and every vehicle in our service fleet is MSHA compliant. In addition to our experience and knowledge, there is no better source for scales, weighing systems and service at your mine site. Contact Southwestern Scale Company Inc for your mining industry-related needs.